On sending an ultrasonic wave from a ship towards the bottom of a sea, the time interval between sending the wave and receiving it back is found to be 1.5 s. If the velocity of the wave in sea water is 1400 ms^-1, find the depth of sea.

Figure below shows the distance-displacement graph of two waves A and B. Compare (i) the amplitude, (ii) the wavelength of the two waves.

The natural frequency of a simple pendulum of length 1.0 m on earth's surface is :

[Take g = 9.8 m/s²]

1. 0.5 Hz
2. 100 Hz
3. 50 Hz
4. 5 Hz

A wire stretched between two fixed supports, is plucked exactly in the middle and then released. It executes (neglect the resistance of the medium) —

1. resonant vibrations
2. natural vibrations
3. damped vibrations
4. forced vibrations.